This invention relates to a method of plating selected surface areas of a plastic or metal part, the method incorporating a permanent polymeric stop-off material on the unplated portions. More particularly, the invention relates to the use of a permanent polymeric plating mask containing poly(isobutly methacrylate) and poly(vinyl toluene).
The electrolytic deposition of metal coatings onto plastic or metal substrates is a well-known industrial art. It is often desirable, particularly where the metal coating is provided for decorative purposes, to plate only selected areas of the surface. Heretofore this has been done by masking the unplated portions with a temporary layer of a polymeric material. The polymeric mask is removed by mechanical or chemical means after plating.
One such masking method is set forth in U.S. Pat. No. 3,451,902. The patent describes a process of electrolytically coating an aluminum sheet wherein the polymeric stop-off material is an acrylic resin. The resin is nonsoluble in acid plating media, but easily removed in alkaline media having a pH of 7.5 or higher. Another method is proposed in U.S. Pat. No. 3,772,161. That patent relates to the application of vinyl toluene-butadiene copolymer masks on platable thermoplastic surfaces. After plating, the mask is removed by a solvent such as a 50/50 blend of mineral spirits and heptane.
Among the problems encountered by these methods have been poor adhesion, degradation, and erosion of the masking layer upon exposure to harsh cleaning and plating chemicals. Thus, it has been necessary to remove the mask after plating. It has also been difficult, or impossible, to form distinct edges between masked and unmasked portions of a part. Moreover, it has not been uncommon for a masking layer to wear through during a plating cycle, causing undesirable deposition of metal onto masked surface portions.
Thus it has been desired to provide a method of masking a plastic or metal article with a permanent, durable, polymeric layer capable of forming clean edges between masked and unmasked surface areas.